Converter for telegraphic signal



desired intelligence by their presence or absence.

in=-response to energy pulses of uniform Width.

polarities.

United States Patent .8 Claims. (Cl. 173--70) This invention relates to conversion apparatus and more particularly to apparatus .for converting a transmitted signal originally containing intelligence into a -train1,of pulses which represent the intelligence originally transmitted.

For'many years intelligence has been transmitted from one.point to distant points in the form of pulses of energy -eIectricaI, sound, etc., which-pulses convey the The original telegraphic codes comprised energy pulses of more than one width or duration but modern automatic telegraphic equipment such as the teletypewriter operate intervals between energy pulses are also maintained constant, and intelligence is conveyed by the relative posi tions of'the pulses and separating intervals. Thus, a

common code for the transmission of intelligence by teletypewriter equipment comprises five equal time periods, each of which periods may or may not contain an energy pulse in accordance with the information transmitted.

The transmission of intelligence by such codes-over short distances may be by wires, and the pulses may be in the form of direct current pulsesof oneor both For long range transmission, however, the pulsesusually comprise an audio frequencyalternating current called a tone. The tone source is keyed in the desired sequence to produce the tone pulses in the desired .form for conveying the intended intelligence, .and the resulting train of pulses may be then used to modulate a high frequency carrier for radio broadcasting or may .be transmitted directly over wires. in either case, the

transmitted signal may be subjected to interference such as by .electrical storms or electrical surges on transmission lines resulting in shortduration hiatuses in the tonepulses and short duration noise pulses in the inter- .vals separating the tone pulses. The .net result is.an undesiredmultiplication.of pulses which often produces garbling of the intelligence by the receiving equipment. A converter for converting the distorted signal into a signal which can be properly utilized by the receiving equipment isnecessary.

.It is, therefore, an object of this invention to provide .apparatus for converting a distorted signal containing intelligence into .a series of undistorted pulses.

:Anotherobject of this invention is toprovide a novel and improved apparatus for converting distortedalternating tone pulses separated by characteristic intervals into direct current pulses and intervals of undistorted character.

A further objectof this invention is to provide apparatus for reconstructing a train of direct current pulses containing intelligence from a distorted alternating current signalof pulses.

Other objects and advantages of the invention will The single figure of the drawing is ablock diagram of the apparatus of this invention.

Structure Referring now to the drawing, the reference numeral 5 designates a teletypewriter or other communication equipment which generates electrical signals representative of intelligence to be transmitted to a distant station. The output of the teletypewriter 5 is connected to the input of a transmitter 7 in which the direct current pulses from teletypewriter '5 are converted into pulses of an audio frequency tone and are then used to modulate :a radio frequency carrier for broadcasting through space.

A receiver 9 picks up the broadcast signals from the transmitter 7 and detects them to eliminate the radio frequency carrier. The output of the receiver 9 is connected to the input of an amplifier .11. The amplified signal output of the amplifier 11 is then applied to a rectifier and filter circuit 13, and the output of the circuit 13 is coupled to a keyed relaxation oscillator 15 which produces rectangular pulses, all of which are of the same amplitude and polarity, from individualkeying pulses from the circuit 13. The output of the relaxation oscillator 15 is applied to an integrating circuit 17 which integrates the pulses produced by the relaxation oscillator IS-into a series of saw-tooth waves and applies the resulting signal in parallel to two transmission channels, a mark channel and a space channel.

The mark channel comprises a limiter 19 controlling the firing of a thyratron 21 which forms an electronic switch, an integratorZ?) for'integrating the pulse output of the thyratron "21, and ajlirniter 25 connected to the output of the integrator 23 and controlling the firingof a thyratron 27.

The space channel comprises a differentiating circuit '31 which diiferentiates the saw-tooth waves from theintegrator 17. The differentiator 31 feeds an integrator 33, the output of which is connected to the input of a limiter 35, which controls the conduction of a thyratron 37 which forms an electronic switch. An integrator 39 is connected to the output of the thyratron 37 and integrates the output therefrom, feeding its output into a limiter 41 which controls the firing of a thyratron 43.

A double-pole, double-throw switch 51 comprising terminals 511155112, 51c, and 51d and switch arms 51e and 51 is connected to the output of the thyratron 27 by terminals 51a and 51c and to the output of the thyratron .43 by terminals 51b and 51d. Since the outputs ofthe thyratrons 27 and 43 are the outputs of the markand space channels respectively, both channels are connected to the switch 51. The switch arm 51e is connected to the input of an integrator 53 which integrates the pulse output fromthe mark or space channels and applies its integrated output to a limiter 55.

A double-pole, double-throw switch-57 comprising ter- -minals 57a, 57b, 57c, and 57d and switch arms 572 and 57] is connected tothe limiter 55 by terminals'57a and 57a and to the switch arm Sif e terminals 57band 57d. The switch arms 57e and-57f'are connected to the inputs of thyratrons 61 and 59 respectively. The outputs of .the converter aretaken from the thyratrons 59. or 61.

The threshold limiters 19, 35, 25, 41 and 55 have their limiting thresholds controlled by appropriate biasing means. In theapparatus illustrated, the limiters 19 .and are both connected to. a common source of negative bias voltage (not shown) by a potentiometer 18 having a wiper arm 34. The threshold of the limiters 19 and 35 may be varied by moving the wiper arm 34 along'the potentiometer :18. The limiters 25 and 41 are similarly controlled by the positioning of a wiper arm along a potentiometer 24, and the limiter is controlled-by a potentiometer 54 .having a wiper arm 56. It is;to .be

modulates a radio frequency carrier wave. lated carrier is radiated from the transmitter antenna and 7 Whenever the apparatus is energized, one thyratron of each pair is conducting. Such circuitry is old and not part of this invention and willnot, therefore, be described herein in greater detail.

Operation The waveform of the signal'output of each stage is illustrated adjacent the output of its respective stage, and

the part of the apparatuswherein any particular waveform is found is indicated by appropriate arrows.

The output from the telet'ypewriter 5 1s a train of direct current pulses which are of a duration predetermined by the machine and are separated by characteristic intervals of no-energy. The particular arrangement, the presence or' the absence, of the pulses conveys the intelligence which 'is to be transmitted. For the purpose of this description,'two adjacent time periods have been chosen to explain the operation of the apparatus. a The waveformof the signal output from the teletypewriter 5 -1is shown as a first time period which contains a direct current pulse and a second time period which contains no energy. Time is considered as increasing from left to right. The beginning and end, of each period is indicated by an index mark at the base line. I

For transmission of the signal by radio'broadcasting, the output of the teletypewriter 5 is applied to the input of the. radio transmitter 7 wherein the direct current pulse is converted to a tone pulse, and the tone pulse The moduis picked up by the antenna of the receiver 9. which detects the signal and eliminates the carrier wave. However, the signal transmitted from the transmitter 7 has been distorted 'in its transmission through space and, as is shown on the drawing, now contains a short duration hiatus in 'the pulse and short duration noise pulses in the period in which there was no pulse.

receiver 9 and applies it to the rectifier and filter 13.

The rectifier and filter 13 convert the alternating tone pulse into a varying direct pulse and filter out some of the higher frequency components. 7 The rectified and filtered signal is then applied to key the relaxation oscillator 15 which produces a series of pulses, all of which have the same amplitude and polarity; each pulse from the rectifier and filter 13 keying the oscillator 15 toproduce one pulse therefrom. The integrator 17 receives'the series of pulses from the oscillator 15 and integrates the pulses into a series of saw-tooth waves, the amplitudes of which vary directly with the duration of the respective pulses which produced them. Although the integrator 17 may be'of any suitable type, a capacitor type ispreferred,

wherein the pulse is applied to a capacitorcircuit having a long time constant. 7 The voltage across the capacitor then increases gradually for the duration of pulse a being integrated. If the capacitor is discharged through a short time constant circuit after the pulse has decayed, the voltage across the capacitor drops sharply, producing the saw-tooth wave illustrated.

The saw-toothoutput of the integrator 17 is applied to the mark and space channels in parallel, and the mark 19 is so biased that it conducts only whenthe applied input signal reaches or exceeds a predetermined amplitude. This predetermined amplitude .is represented by the dashed line which'crosses thesaw-tooth wave from the integrator 17. Therefore, the limiter 19 conducts in response to only the two larger saw-tooth waves illustrated.

These waves represent the two portions ofth'e original the teletypew riter 5, but'both are displaced in time'due 7 applied thereto.

tone pulse which was divided in two by interference. The output of the limiter 19 then comprises two rectangular pulses; one comparatively wide and the other narrow; in the first time period. When these two pulses are applied to the thyratron 21, they, initiate conduction through tude of each pulse depending upon the amplitude and V discharge time of the pulse from which it was formed.

Since the diiferentiator produces'a sharp pulse for each rapid change in the amplitude of the applied signal, the sharp pulses are produced by the decay of the saw-tooth waves from the integrator 17, and the greater'the rate of change of the saw-tooth, the higher and wider the differential pulse will be. The differential pulses from the difierentiator 31 are applied to the input'of the integrator 33 which produces a saw-tooth wave for each pulse V The train of saw-tooth waves from the integrator 33.is not the same as the train of saw-tooth waves from the integrator 17, Sinceithe pulse from the diiterentiator 31, which pulse isone from which the saw-tooth waves from the integrator 33.. are formed, is the result of the'trailing edge of the saw-tooth wave from the integrator 17, the leading edge of the saw-tooth Wave from the integrator 33 occurs at the same time as the trailing edge of the saw-tooth wave from the integrator'17. V

The saw-tooth waves from the integrator 33 are applied to the input of the limiter 35 which responds'to that portion of the saw-tooth which is above the dashed line.

Conduction through the limiter 35 produces a pulse which decayed, when the thyratron 37 is triggered, the thyratron 21 has been conducting for a period of time.

' For this discussion, it is assumed that the thyratrons 37 'and'43 have been conducting due to triggering by preceding cycles. When the first pulse of the illustrated cycle is applied to the thyratron 21, that thyratron begins I 'toconduct, cutting-'ofi'conduction through the thyratron 37 and producing a first outputpulse. Whenthe first pulse from the limiter-35 is applied to the thyratron 37, which pulse occurs at a later time than'the first pulse from the limiter 19' as explained above, the thyratron 37 begins conducting, cutting-off conduction through thethyratron 21. The second pulse from the limiter 19 then triggers the thyratron 21 which fires and terminates conduction through the thyratron 37. The conduction through the 'thyratron 21 ceases when a succeeding pulse from the limiter 35 triggers the thyratron 37, and the thyratron' Y 21does not again begin to conduct or cut-off the thyra' tron'37 until the succeeding cycle. The output of the thyratron 21 comprises two complete pulses within the two periods illustrated and the output of the thyratron 37 comprises a final portion of a pulse at the beginning of the first time period, a short complete pulse in the first time period, and an initial portion of a pulse during '5 the second time period.

The outputs of the thyratrons 21 and 37 are then applied to integrators 23 and 39 respectively where the saw-tooth waves are produced from the applied pulses. The limiters 25 and 41 are each adjusted to conduct above the threshold voltage represented by. the dashed lines on the drawings. The limiters 25 and 41 then produce only one output pulse each.

representative of the original signal pulse produced by The output of only on those portions of the saw-tooth waves which are to the operation of the apparatus. Since the limiters 19, 35, 25, and 41 respond to portions of the saw-tooth waves which occur later than the leading edges of these waves, the resulting output from the limiters is delayed in phase from the original signals which produced the output. The apparatus operates the same for all the cycles applied to itand each cycle will be delayed by the same amount so that the resulting reconstructed signal will be the same as the original signal except in phase. Since all the components, the pulses and the intervals, are present in the final signal in the same order and of the same duration as those in the original signal, no intelligence is lost by thedelay. -However, should time distortion or changes in the phasing of the signal be desired, the switches 51 and 57 and the integrator 53 and the limiter 55 are provided.

The outputs from the thyratrons 27 and 43 are applied to terminals 51a and 51d and to 5112 and 510 respectively, and, depending on the positions of the switch arms 51a and 51 either output may be applied to the integrator 53 and limiter 55. The relative durations and phasing of the pulses from the thyratrons 27 and 43 may be varied by changing the threshold of'the limiter'SS, thus controlling the time at which the thyratrons 59 or 61, whichever is connected to the limiter 55, fires and also the length of time during which it conducts. Since the time of initiation of conduction through that thyratron which is connected to the limiter '55 controls the time of termination of conduction through the other thyratron, if the firing of one thyratron is delayed, the pulse output from the other is lengthened. The arms 51e and 51 and the arms 572 and 57 are all mechanically ganged to be moved together to connect either the output of the mark or of the space channel through the integrator 53 and the limiter 55.

Since there will always be some point at which a received pulse ends, the difierentiator 31 will always produce a sharp pulse which represents the end of the received pulse. This sharp pulse will serve to fire the thyratrons 37, 43 and 59 in the space channel and terminate conduction of the thyratrons 21, 27 and 61 in the mark channel. Therefore, the mark channel will produce an output pulse of approximately the desired duration and the space channel will produce pulses of the desired duration and representative of the intervals between the pulses of the mark channel. Since only one channel can produce a pulse output at any time, the pulses of the space channel determine the intervals of the mark channel. Thus, the two channels of the apparatus operate together to produce an undistorted signal which is the substantial duplicate of the original signal from the teletype writer 5.

The apparatus of this invention will operate to reconstruct a train of pulses of predetermined duration separated by characteristic intervals from a badly distorted signal, even though that signal be alternating. The reconstructed pulse train may safely be applied to modern printing or teletypewriter equipment without fear of garbling; saving time and accomplishing the primary mission of the equipment.

Obviously many modifications and variations of the present invention are possible in the light or" the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for converting a distorted signal which contains intelligence in the form of pulses of predetermined duration separated by characteristic intervals into a series of pulses all of which are of the same amplitude and polarity and of said predetermined duration and separated by said characteristic intervals, said signal having been distorted by interference therewith resulting in pulses in said intervals and hiatuses in said pulses; said apparatus comprising means for creating a series of first saw-tooth waves from said distorted signal, each of said first saw-tooth waves being created from oneof said pulses of said distorted signal and having a maximum amplitude which is directly dependent upon theamplitude and duration of said one signal pulse; a first transmission channel and a second transmission channel, .said first saw-tooth waves being applied to said first and second channels in parallel; first electronic switch means in said first channel, said first elctronic switch means being adapted to remain in the conductive or the non-conductive state until changed by external means; first initiating means in said first channel for initiating conduction through said first electronic switch means, said first initiating means being responsive to said first saw-tooth waves which exceed apredetermined amplitude; differentiation means in said second channel for differentiating said first saw-tooth waves into sharp pulses; integrating means in said second channel connected tosaid difierentiation means for integrating said sharp pulses into second saw-tooth waves the amplitudes of which are directly dependent upon the amplitudes and durations of said sharp pulses; second-electronic switch means in said second channel, said second electronic switch means being adapted to remain in the conductive or non-conductive state until changed by external means; second initiating means in said second channel for initiating conduction through said second electronic switch means, said ,second initiating means being responsive to said second sawtooth waves whichexceed a predeterminedamplitude; said first and second switch means being so interconnected that the initiation of conduction through one electronic switch means terminates conduction through the other elecronic switch means.

2. The apparatus defined in claim 1 wherein said first and second initiating means comprise'threshold limiters so biased asto conduct only when the amplitudes of the applied saw-tooth waves overcome the bias, .said amplitudes for said first and second initiating meansbeing greater than the maximum amplitude of the saw-tooth waves generated from said short duration pulses in said intervals and from the short duration hiatuses in said intelligence pulses, whereby said initiating means and said respective electronic switch means do not change their states in response to said respective short duration pulses or hiatuses.

3. Apparatus for reconstructing a train of direct currentpulses of predetermined duration separated by precise characteristic time intervals from an alternating signal comprising tone pulses representative of said direct current pulses and periods of no-tone representative of said intervals, said signal having been distorted by interference in such a manner that said periods contain noise pulses and said tone'pulses contain hiatuses; said apparatus comprising keyed oscillator means responsive to said alternating signal for generating a train of direct curent pulses of like amplitude and polarity of said generated pulses being coincident in initial phase and duration with its keying pulse; first means connected to said oscillator means for integrating said generated pulse train into a series of first'triangular waves related individually to the pulses of said pulse train, the amplitude of each of said first triangular waves being dependent upon the duration and amplitude of the generated pulse from which it is formed; a first transmission channel and a second transmission channel, said series of first triangular waves being coupled to said first and second channels in parallel; said first channel comprising first means for producing individual rectangular pulses in response to said first individual triangular waves which exceed a predetermined minimum amplitude, said first rectangular pulses being related in initial phase and duration to the amplitude of said respective first triangular waves from which they are formed; first thyratron means in said first channel connected to said first rectangular pulse producing means and responsive to said 6 r first rectangular pulses to fire; said second channel. comprising means for differentiating said series of firsttriangular waves into a series of sharp pulses; second means connected to said differentiating means for integrating said sharp pulses into a series of second triangular waves, the amplitude of'said second triangular waves being dependent upon the amplitude and duration of the respective sharp pulses from which they are formed;

second means responsive to said second individual triangular waves which exceed a predetermined minimum amplitude for producing second individual rectangular waves related in'initial phase and duration to the amplitudes of the respective second triangular waves from which they are formed; and second thyratron means connected to said second rectangular wave producing means and responsive to said individual rectangular waves to fire; said first and second'thyratron means being so interconnected that the firing of one thyratron means terminates conduction through the other thyratron means.

7 4. The'apparatus defined in claim 3 wherein said first and second rectangular wave producing meanscomprise threshold limiters so biased as to conduct only "when the amplitudes of the applied triangular waves overcome the respective biases, said amplitudes for producing conduction through said first and second rectangular pulse producing means being greater than the maximum amplitudes of the triangular waves generated by said hiatuses in said tone and by said noise pulses in said intervals,

whereby said respective thyratron means do'not fire, in

response'to said respective short duration noise pulses or hiatuses. V v

'5. Apparatus for converting an alternating signal into a train of direct current pulses representing intelligence, said alternating, signal comprising tone .pulses of pre- 7 determined duration separated by precise intervals, said 7 signal being distorted by interference which produces hiatuses in said tone pulses and sharp pulses in said in:

tervals; 'said apparatus comprising means for receiving said alternating signal; means connected to said receiving means for converting said alternating signal into a train of first pulses all ofwhich'are 0f the same amplitude and polarity, first pulses being produced for each 1 said noise and intelligence pulse; first means for integrating said first pulses into'a series of first saw-tooth waves having maximum amplitudes which are directly dependent upon the durations of the respective first pulses from which they are formed; a firstchannel and a second channel; means for applying said first saw-tooth waves to said first and'second channels in parallel; said first channel comprising a first threshold limiter biased to conduct only on the peaks of said first saw-tooth waves which exceed a predetermined amplitude; and a first thyratron connected to said first limiter, conduction through said first limiter initiating conduction through said first thyratron; said second channel comprising a diflerentiation circuit for difierentiating said first 'sawtooth waves into respective sharp pulses; a second means connected to said' differentiationcircuit for integrating said sharp pulses into a series of second saw-tooth waves having peak amplitudes which are directly dependent upon the durations and amplitudes of the respective first pulses from which they are formed; ,a second threshold limiter biased to conduct only on the peaks of said second saw-tooth waves which exceed a predetermined, amplitude; and a second thyratron connected to said second limiter, conduction through said second limiter initiat: ing conduction through said second thyratron, said first and second thyratrons being so interconnected that initiation of conduction through one terminates conduction through the other.

6. The apparatus defined in claim 5 further including a third integrating means connected to said first thyratron; a third threshold limiter connected to said third integrating means; and a third thyratron connected to said u third limiter, the functions of said third integrating means,

third limiter and third thyratron being'the same as the functions of said first integrating, means, first limiter andw first thyratron.

7. The apparatus defined in claim 6 further including a fourth integrating means connected to' said second thyratron; a fourth threshold limiter connected 'to said fourth integrating means; and a fourth thyratron connected to said fourth limiter, said fourth integrating means, fourth limiter and fourth thyratron functioning the sameras said second integrating means, second limiter and second thyratron.

8. The apparatus defined in claim 7 further including a first double-pole double-throw switch comprising a first pair of switch arms and first and second pairs of switch terminals, the output of said third thyratron being connected to said first pair of switch terminals in parallel,

said fourth thyratron being connected to said second pair of switch. terminals in parallel, said first pair of switch arms contacting one pair of said first or secondpairs of switch terminals at any time, a fifth integrating means, a fifth threshold limiter connected to said fifth integrating means, one of said first pair of switch arms being connected to the input to said fifth integrating means, a second double-pole double-throw switch comprising a second pair of switch arms and third and fourth pairs of switch terminals, the other of said first pair of switch arms being connected to said fourthpair of switch terminals, the output of said fifth limiter being connected to said third pair of switch terminals, fifth and sixth thyratrons, theinput of said fifth thyratron being connected to one of said second pair of switch arms and the input to said sixth thyratron being connected to the other of said second pair of switch arms, said first and second pair of switch arms being operatively ganged together.

References Cited in the file of this patent UNZTED STATES PATENTS 2,470,722 Rattner May 17, '1949 2,552,126 7 Van Duuren May 8, 1951 2,611,824 Van Duuren Sept. 23, 1952 FOREIGN PATENTS 77 683,607 Great Britain Dec. 3, 1952 

